Investigations of Solvent Systems Based on bis-triazine-bipyridine (BTBP) - class Ligands for the Separation of Actinides from Lanthanides

Doctoral thesis, 2009

Shortages of fossil fuel and other political movements contributed to the nuclear energy “renaissance”. Nuclear energy, however, is not free of challenges, one of them being nuclear waste management. The “once-through” cycle, where the nuclear fuel is used once in the reactor, cooled and finnaly disposed for about 100 000 years is currently used in most of the world. Reprocessing is another alternative, by making new fuel from separated uranium, MOX (Mixed Oxyde fuel). However, the storage time remains the same. An alternative to the storage time and radiotoxicity is partitioning and transmutation (P&T) concept. Transmutation is defined as the transformation of one radionuclide into another by changing its nuclear structure. The partitioning is the process of separation nuclides from the rest of the waste and involves a separation process which utilize an organic solvent containing one or several molecules and a diluent for extraction purposes. Among the last extractant families developed in Europe, used for partitioning, the 6,6’-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo[1,2,4]triazin-3-yl)-[2,2’]bipyridine (BTBP) is the most promising molecule for an eventual industrial application. The present work focuses on several aspects insufficiently studied before in relation to a BTBP based extraction system. These aspects include: the importance of the diluents regarding both the extraction capabilities of the formed system with different metals, the role of the diluents in complex formation , the importance of the side groups added to the molecule to facilitate dissolution, easing the phase transfer and thus enhancing the extraction capabilities and also the role of the side groups in complex formation.